Ionomer resin materials are generally used for their durability in golf ball inner cover and outer cover layers. For example, when golf balls include an outer cover layer formed from a conventional ionomeric material, the golf ball provides a good combination of distance and durability. But, because conventional ionomer-covered golf balls have a hard “feel” and lower spin rate when struck with a club, golf ball manufacturers typically replace the ionomer cover with a softer cover formed from polyurethane or polyurea. The softness of the polyurethane and polyurea materials is generally balanced with a harder inner cover or intermediate layer. However, golf ball covers made from polyurethane have not, to date, fully matched ionomer-covered golf balls with respect to resilience or the rebound of the golf ball cover
In addition to polyurethane, there are generally two other ways to obtain a soft golf ball cover. First, a very low modulus ionomer (VLMI) can be used to make a cover with a low compression, i.e., a soft “feel”. In fact, U.S. Pat. No. 4,431,193 relates to a golf ball having a multilayer cover wherein the inner layer is a hard, high flexural modulus ionomer resin and the outer layer is a soft, low flexural modulus ionomer resin. While the VLMI provides a soft cover, the coefficient of restitution is also very low, which results in a “dead” feeling when struck with a club. Blends of ionomers and nonionomers, e.g., grafted metallocene-catalyzed polyolefins, such as those disclosed in U.S. Patent Publication No. 2003/0078348, have also been used to produce soft cover layers in golf balls: Less material is typically required to obtain the desired degree of softness when FUSABOND®, a series of maleic anhydride grafted ethylene-butene or ethylene-octene metallocene catalyzed copolymers commercially available from DuPont having flexural modulus values between about 2000 psi and 3000 psi, is used as a cover layer as compared to a VLMI resin. In addition, the use of FUSABOND®, or a similar material, results in a golf ball with a good balance of speed and spin. Due to the hydrophobic nature of the polymer backbone, however, it is essential that good mixing is achieved to enhance compatibility between FUSABOND® and conventional ionomers and to avoid processing problems. Moreover, there is increased potential for delamination due the metallocene's absorption of moisture.
Thus, it would be advantageous to produce a composition that reduces processing and compatibility issues, provides increased adhesion to other materials, results in a good balance of speed and spin, and delivers a softer “feel” when struck with a club compared to conventional ionomer resins. In addition, there remains a need in the golf ball art for a material that provides a good balance of softness, e.g., low flexural modulus, and resiliency. The present invention provides a composition that is resilient, but soft, and, in addition, golf balls formed with the compositions of the invention have reduced processing issues, and increased adhesion to other golf ball layers.